changeset 608:c4c1544e9b7b

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Make GF256 hashable in Python 2.6.
Python 2.5 has a default fallback where id(x) was used if x had not
__hash__ method, but in Python 2.6 one gets the error
exceptions.TypeError: unhashable type: 'GF256'
instead. Defining a suitable __hash__ method solves this.